In order to inspect positional error of a board having a surface formed with a conductive pattern, there has been known an optical or mechanical method for sensing, for example, the leading edge of the board being transferred.
There has also been employed a method in which two pairs of sensors are located, respectively, at orthogonally intersecting portions of a conductive pattern formed on the surface of a board to detect positional displacement of the board in accordance with the difference between sense signals from the sensors, as disclosed in Japanese Patent Laid-Open Publication No. 10-311861.
However, the optical sensing method involves a problem of difficulty in high-accuracy detection due to variation in detection level caused by deterioration in light-emitting means or changes in surrounding atmosphere. The same problem is observed in the mechanical sensing method.
In the method disclosed in the Japanese Patent Laid-Open Publication No. 10-311861, a board is located and fixed at a given position of an apparatus for inspecting the conduction of a wiring pattern, and then the two pairs of sensors each having a width about one-half of the line width of the conductive pattern are disposed, respectively, at portions of the conductive pattern orthogonally intersecting in the X-direction and the Y-direction. Therefore, due to the requirement of providing four high-precision sensors each having a width about one-half of the line width of the conductive pattern, the method is limited to only a particular application.
Thus, it is desired to achieve a board-displacement detection apparatus capable of being arranged at a desired position on a transfer path in a simple structure while maintaining a high degree of accuracy without variation over time.
It is therefore an object of the present invention to provide a board-displacement detection apparatus and method capable of solving the above problems, for example, capable of being arranged at a desired position on a transfer path in a simple structure while maintaining a high degree of accuracy without variation over time.